Electrical DC switching system

Abstract

An electrical DC switching system for extinguishing an electric arc, wherein the electrical DC switching system includes: a main contact arrangement having a first contact and a second contact, the main contact arrangement being operable between a closed position and an open position, a plurality of serial contacts connected in series with each other and connected in parallel with the main contact arrangement, each serial contact being operable between a closed position and an open position, wherein in a current breaking operation the main contact arrangement is configured to be set in the open position before the plurality of serial contacts are configured to be set in their open positions, and a current injection circuit including a resonance circuit configured to be connected across the serial contacts, and a first switch configured to be switched between an open state and a closed state and configured to be connected to the resonance circuit and to the serial contacts, wherein the first switch is configured to be set in the closed state when the serial contacts are in their open positions to enable an injection current to flow through the resonance circuit and into the serial contacts in a first flow direction which is opposite to a flow direction of an arc current flowing through the serial contacts.

The invention claimed is: 
     
       1. An electrical DC switching system for extinguishing an electric arc, wherein the electrical DC switching system comprises:
 a main contact arrangement having a first contact and a second contact, the main contact arrangement being operable between a closed position and an open position, 
 a plurality of serial contacts connected in series with each other and connected in parallel with the main contact arrangement, each serial contact being operable between a closed position and an open position, 
 wherein in a current breaking operation the main contact arrangement is configured to be set in the open position before the plurality of serial contacts are configured to be set in their open positions, and 
 a current injection circuit including a resonance circuit configured to be connected across the serial contacts, and a first switch configured to be switched between an open state and a closed state and configured to be connected to the resonance circuit and to the serial contacts, wherein the first switch is configured to be set in the closed state when the serial contacts are in their open positions to enable an injection current to flow through the resonance circuit and into the serial contacts in a first flow direction which is opposite to a flow direction of an arc current flowing through the serial contacts, 
 wherein each serial contact, consists of a non-magnetic material. 
 
     
     
       2. The electrical DC switching system as claimed in  claim 1 , wherein the main contact arrangement consists of a silver or a silver alloy. 
     
     
       3. The electrical DC switching system as claimed in  claim 1 , wherein the non-magnetic material is brass or zinc. 
     
     
       4. The electrical DC switching system as claimed in  claim 1 , wherein the resonance circuit includes a capacitor and an inductor. 
     
     
       5. The electrical DC switching system as claimed in  claim 4 , wherein the current injection circuit includes a DC power source configured to charge the capacitor when the first switch is in the open position. 
     
     
       6. The electrical DC switching system as claimed in  claim 1 , comprising:
 a control system, 
 wherein the current injection circuit includes a second switch connected to the resonance circuit and to the serial contacts, wherein the second switches is configured to be switched between an open state and a closed state, wherein in the closed state the second switch is configured to enable current to flow through the resonance circuit in a second flow direction opposite to the first flow direction, and 
 wherein the control system is configured to alternatingly first set the first switch, and then the second switch, first in the closed state and then in the open state upon a current breaking operation, until a current pulse, emanating from energy supplied by the arc current, flowing through the resonance circuit and into the serial contacts reaches an amplitude which is equal to or greater than a magnitude of the arc current. 
 
     
     
       7. The electrical DC switching system as claimed in  claim 6 , wherein in each iteration of alternatingly first setting the first switch, and then the second switch, first in the closed state and then in the open state, the control system is configured to:
 set the first switch in the closed position, enabling a first current pulse to flow through the resonance circuit in the first flow direction, 
 set first the first switch in the open state and then the second switch in the closed state when the first current pulse has become zero to enable a second current pulse to flow through the resonance circuit in the second flow direction, and 
 to set the second switch in the open state when the second current pulse first has become zero. 
 
     
     
       8. The electrical DC switching systems as claimed in  claim 6 , wherein the second switch is connected across the resonance circuit. 
     
     
       9. The electrical DC switching system as claimed in  claim 1 , comprising a varistor connected in parallel with the main contact arrangement. 
     
     
       10. The electrical DC switching system as claimed in  claim 2 , wherein the non-magnetic material is brass or zinc. 
     
     
       11. The electrical DC switching system as claimed in  claim 2 , wherein the resonance circuit includes a capacitor and an inductor. 
     
     
       12. The electrical DC switching system as claimed in  claim 2 , comprising:
 a control system, 
 wherein the current injection circuit includes a second switch connected to the resonance circuit and to the serial contacts, wherein the second switch is configured to be switched between an open state and a closed state, wherein in the closed state the second switch is configured to enable current to flow through the resonance circuit in a second flow direction opposite to the first flow direction, and 
 wherein the control system is configured to alternatingly first set the first switch, and then the second switch, first in the closed state and then in the open state upon a current breaking operation, until a current pulse, emanating from energy supplied by the arc current, flowing through the resonance circuit and into the serial contacts reaches an amplitude which is equal to or greater than a magnitude of the arc current. 
 
     
     
       13. The electrical DC switching system as claimed in  claim 7 , wherein the second switch is connected across the resonance circuit. 
     
     
       14. The electrical DC switching system as claimed in  claim 2 , comprising a varistor connected in parallel with the main contact arrangement.